In another development the Syrian state news agency SANA is reporting that ISIL fighters have attacked Deir al-Zour military airport with “rockets carrying mustard gas causing some people to suffocate.”

Swathes of Deir al- Zour City in the north east of the country have been besieged by ISIL for months.

The UN has begun a programme of aid drops to the 200,000 people trapped within the city.